A semiconductor wafer which is intended to be suitable in particular for the fabrication of electronic components with line widths of less than or equal to 0.13 μm must have a large number of special properties. Taking a bipolar IC as a typical example of their applications, those under use are the semiconductor wafer by the vapor-phase growing of an epitaxial layer of doped silicon having a thickness of several micrometers on a mirror-polished wafer of low-resistivity grade. The number of crystal defects in such semiconductor wafer on which semiconductor components are intended to be produced is critical to the semiconductor device yield. When crystal defects are present in a certain number and size, crystal defects can lead to the failure of the components.
On the other hand, the film thickness of the epitaxial layer of silicon is, though widely varied depending on the intended particular application field, in the range from 1 to 15 μm for the bipolar ICs and bipolar CMOSs as an example for those having a relatively small thickness or several tens of μm for the discrete as those having a relatively large thickness and, as a trend in recent years, those under manufacturing include those of the submicron range having a thickness not exceeding 1 μm for the small thickness and those exceeding 100 μm for IGBTs for the large thickness.
Preparation of the aforesaid semiconductor wafer with an epitaxial layer is performed in such a way that a silicon single crystal rod pulled up by the Czochralski method from a melt of silicon admixed in advance with a dopant so as to give a specified type of electro conductivity and appropriate resistivity is subjected to cylindrical grinding with the axial line of the direction of pulling up as the axis of rotation followed by a shaving work on the cylindrical periphery along the direction of the axial line to serve as an orientation flat of the wafers and then slicing in a direction perpendicular to the axis of the rod to give sliced wafers from which a chemically etched wafer is obtained after the works such as chamfering, lapping on both flat surfaces, chemical etching and the like and the chemically etched wafer is subjected to mirror polishing.
There is a need to produce a semiconductor wafer with an epitaxial layer formed on an active surface thereof and having sufficient low crystal defect density so as to raise the semiconductor device yield.
Like reference symbols in the various drawings indicate like elements.